4. RESPIRATORY DISTRESS SYNDROME Flashcards
Definition of RDS
RDS is a respiratory disorder usually developing in the first few hours of life in premature infants <36 weeks AOG
It was first described as HYALINE MEMBRANE DISEASE in 1903 due to the presence of proteinaceous exudates along the walls of the alveoli on histopathologic sections
It is difference from Acute RDS w/c is primary seen in adults
The primary cause of RDS is related to:
1.
2.
- Structural lung immaturity in preterm infants
accompanied by
- Quantitative or qualitative deficiency in pulmonary surfactant
Incidence
Generally, the incidence and severity of RDS increases with decreasing AOG. The risk being highest in extremely preterm infants. It is a major cause of morbidity and mortality in preterm infants.
Incidence wise, RDS occurs in:
60 to 80% of infants <28 weeks AOG
15 to 30% of those between 32 to 36 weeks
And rarely in the >37 weeks
What are the factors that increase the risk of RDS?
- Gest DM, Maternal Infection
- Perinatal asphyxia (causes acute lung injury)
- Cesarean deliver (lower activity of Amiloride-sensitive Na+ channels in alveolar epithelium leading to reduced fluid clearance)
- Precipitous deliver
- Multiple births
- Cold stress (decreased surfactant production)
- Maternal history of previously affected infant
Factors that decrease the risk of RDS
- Chronic or pregnancy-associated HTN (chronic stress accelerates fetal lung maturation)***
- Maternal heroin use (increases surfact production by promoting binding of choline to phosphate)
- Prolonged ROM - conflicting
- Antenatal corticosteroid prophylaxis***
T/F. Preeclampsia decreases the risk for RDS
T
Pathophysiology of RDS
Knowledge Of the normal fetal of development is vital to understanding the pathophysiology of neonatal RDS which is juju inadequate surfactant activity resulting from lung immaturity.
Normal fetal lung development occurs in four stages
- Embryonic (26 to 33 days)
- Pseudoglandular (5th to 16th week)
- Canalicular (16th to 25th week)
- Saccular (25th to 2 years)
It is during the CANALICULAR STAGE that respiratory bronchioles and alveolar ducts are formed allowing gas exchange with the surround capillaries.
At around 25 wks AOG, cuboidal epithelial cells begin to differentiate into alveolar type II cells with formation of cytopplasmic lamellar bodies, the presence of which corresponds to the earliest surfactant production.***
However, it is not until the 35th week AOG that enough surfactant is produced necessary to prevent RDS.
During the SACCULAR stage, gas exchange becomes more effective as saccules subdivide into anatomic alveoli.
These alveoli increase from 0 to 32 weeks AOG they increase up to 50 to 150 million at birth in term infants “ALVEOLARIZATION”
Alveolar growth continues for at least 2 years after birth reaching about 300 million alveoli in adults.
PULMONARY SURFACTANT
As mentioned, the primary cause of RDS is deficiency of pulmonary surfactant, which is developmentally regulated.
Because it is developmentally regulated, it follows that the most common cause of surfactant deficiency is preterm delivery. Surfactants may also be inactivated by meconium (in term) and blood
In terms of composition, pulmonary surfactant consists of 90% lipids, 80% of which are phospholipids composed primarily of DIPALMITOYLPHOSPHATIDYLCHOLINE, phosphatidyl glycerol and inositol. 10% of these lipids are cholesterol.
The rest 10% is composed of surfactant-specific apoproteins which contribute to the biophysical surface tension decreaseing properties (SP-A, SP-B, SP-C, SP-D)
SP-A - responsible for tubular myelin formation than contributes to the surface film within the alveoli (also a non0immune host defense protein & regulator ofinflammation)
SP-B - mostly contributes to surface tension lowering property since it facilitates surface absorption of lipids
-hereditary deficiency in males is FATAL due to loss of lamellar bodies
After being secreted, surfactants move from airspaces back to type II alveolar cells for recycling and contributes to the intracellular surfactant pool (omg so bumabalik pala siya)
With adequate surfactant activity, high surface tension within the alveolar wall develops leading to —> instability of the lungs at end-expiration, low lung volume and decreased complaiance.
LAW OF LAPLACE = distending pressure = 2T surface tension/radius
The resulting atelectasis leads to V/Q mismatch impairing efficient gas exchange.
Hypoxemia and hypercarbia develop with subsequent metabolic & respiratory acidosis. Acidosis decreases surfactant production.
Combination of these factors leads to Pulmonary Vasoconstriction compromising blood flow to the alveoli
With chronic administration of high flow O2, BAROTRAUMA ensues
Alveolar epithelial and capillary endothelial cells become damaged. INFLAMMATION ensues. INflammatory mediators enhance conversion of surfactant to its inactive vesicular form.
Eventually, lung injury becomes irreversible and there will be bronchopulonary dysplasia characterized by a “bubbly lung pattern” on CXR seen as
(+) Focal areas of radiolucency representing normal lung parenchyma
(+) curvilinear densities representing FIBROSIS (normally aerated lung trapped between fibrotic changes
This must be differentiated from WILSON-MIKITY SYNDROME - a syndrome characterized by pulmonary dysmaturity wherein alveoli do not mature at the same time
(+) Focal areas of radiolucency represent mature distended alveoli
(+) Curvilinear densities represent immature collapsed alveoli
Differentiating factor would be based on HISTORY
BPD - (+) history of RDS and high O2 administration
WMS - (-) history of RDS and high O2 administration
Clinical Manifestations of RDS
Clinical manifestations of RDS result primarily from 1) abnormal pulmonary function and 2) hypoxemia
(Yung isa sa lungs yung isa sa blood distribution)
Common signs and symptoms include:
- Difficulty in initiating normal respiration
- Tachypnea
- Nasal flaring
- Expiratory grunting** - neonate’s attempt to maintain FRC by forefully closing the glottis (Functional residual capacity, is the volume remaining in the lungs after a normal, passive exhalation)
- Retractions - during inspiration, the highly compliant chest wall is drawn inward by the high negative intrathoracic pressure required to expand the poorly compliant lungs
- Apnea - sign of respiratory fatigue in severe RDS
- Cyanosis - reflects an increase in deoxygenated hemoglobin due to hypoxia
- Decreased activity - due to hypoxia or attempt by infant to conserve energy
**inconsistencies sa APGAR
Decrease in grunting may be the first sign of improvement
On PE, auscultation may reveal decreased breath sounds, infant may be pale with diminished peripheral pulses
UO often low in the first 24-48 hours
Peripheral edema is common
What causes the infant’s GRUNTING & RETRACTIONS?
Expiratory grunting** - neonate’s attempt to maintain FRC by forefully closing the glottis (Functional residual capacity, is the volume remaining in the lungs after a normal, passive exhalation)
5. Retractions - during inspiration, the highly compliant chest wall is drawn inward by the high negative intrathoracic pressure required to expand the poorly compliant lungs
Diagnosis
PRENATAL and POSTNATAL
In the diagnosis of RDS, A good prenatal, birth and neonatal transition history is crucial more than that of the physical examination findings which are non-specific. History should also include the different risk factors.
In fact, in a pregnant woman expected to deliver preterm, letter RDS must already be anticipated an appropriate interventions be prepared.
PRENATAL
Prenatally, lung maturity may be determined by assessing the amniotic fluid LECITHIN to SPHINGOMYELIN (L:S ratio). A value of more than 2:1 is indicative of lung maturity.
Another test is the Foam Stability Index or Clement’s Test. In the presence of ethanol, a non-foaming competitive surfactant, the presence of complete ring of bubbles at the meniscus (stable foam) is suggestive of fetal lung maturity.
Lamellar bodies on the amniotic fluid can also be quantified using the same machine used to count platelets (coulter counter placed on platelet mode) and values >50,000/uL are suggestive of fetal lung maturity.
These tests are not routinely performed because of its invasiveness posing risks to the fetus.
Other tests include amniostat, microviscosity and OD at 650 nm.
Newer modalities include use of 3D ultrasound to assess fetal lung maturity. Parameters being measured are:
- Fetal lung volume (FLV) - >50 mL
- Fetal lung-to-liver intensity ratio (FLLIR) - >1.1
- Breathing - related nasal fluid flow (BRNFF)
POSTNATAL
Postnatally, The diagnosis of this disease is based on a clinical picture of a preterm infant with an acute onset of progressive respiratory failure shortly after birth this in conjunction with a chest radiograph.
CXR include:
(+) LOW LUNG VOLUME
(+) CLASSIC DIFFUSE RETICULOGLANDULAR GROUND GLASS PATTERN WITH AIR BRONCHOGRAMS. Peripherally located patent terminal bronchioles.
Alveolar atelectasis contrasting with aerated airways.
On severe RDS, there may be homogenous opacification of both longs (+) WHITE OUT PATTERN
Pneumothorax and air leaks are uncommon findings in the initial CXR and are more commonly observed when lung compliance improves
Other ancillary tests may be requested to rule or to differentiate RDS from other causes of respiratory distress.
This may include CBC, Blood culture, 2d-Echo, Blood glucose, etc
Differential Diagnosis would include:
Give 4
- Transient Tachypnea of Newborn
- Neonatal Pneumonia
- Cyanotic Congenital Heart Disease
- Non-pulmonary systemic disorders
- Transient Tachypnea of Newborn
This is d/t delayed resorption of fetal lung fluid and is generally seen in more mature infants who were delivered through CS without labor.
This is because it is during LABOR when lung fluid started to be reabsorbed.
In addition, during vaginal deliveries, the vagina can squeeze the excess fluid out from the lungs. The major presenting symptom is (+) persistently elevated RR with milder respiratory distress than RDS
It is self-limited and mostly resolves within 6-8 hrs with significant clinical improvement.
On CXR, there is hyperaeration & prominent pulmonary markins (linear densities representing engorged lymphatic vessels trying to remove excess fluid)
- NEONATAL PNEUMONIA
It is often difficult to differentiate between in the fence with letter RDS and those with bacterial pneumonia due to overlap of both clinical and radiographic findings. A good maternal history is very important. There should also be a high index of suspicion. We should investigate for urinary tract infection, premature rupture of membranes for patients that are usually term > 18 hours, Chorioamnionitis, foul discharge, Maternal fever. Also because of this overlap, blood cultures or trachal cultures must be obtained in all preterm infants presenting with respiratory distress. Empiric Antibiotic should be given that will cover common organisms while waiting for the results of the culture. GBS, E.coli, Listeria monocytogenes, Klebsiella sp., Enterococcus
AMPICILLIN + GENTAMICIN is the DOC that will cover all these organism. - CYANOTIC CONGENITAL HEART DISEASE
Most patients with cyanotic congenital heart disease have mild or respiratory distress than that seen in RDS. In addition there is also the absence of characteristic chest x-ray findings in RDS. If the lung function does not improve with respiratory support and surfactant administration, a 2-D echo Should be done throughout structural heart disease or persistent pulmonary hypertension of newborn.
4. NON-PULMONARY SYSTEMIC DISORDERS Several non-pulmonary systemic disorders may also present with respiratory distress 1. Hypothermia 2. Hypoglycemia 3. Anemia/Polycythemia 4. Metabolic acidosis
Appropriate laboratory tests may be requested such as blood glucose, CBC and ABG
Management
Preventive Measures
Generally, the best way to prevent RDS is to prevent preterm delivery. However, this is not always possible. Thus, we can administer ANTENATAL CORTICOSTEROIDS to the mother to accelerate fetal lung maturation and prevent or decrease the severity of RDS.
Antenatal corticosteroids should be administered to all pregnant women who are on their 24 to 34th week age of gestation who are at increased risk of preterm delivery within 7 days.
Either BETA or DEXAMETHASONE can be given
But BETAMETHASONE has the added benefit of decreasing the risk of PERIVENTRICULAR LEUKOMALACIA and has been proven to be more effective in preventing RDS
Doses:
BETAMETHASONE 12 mg IM q24 x 2 doses
DEXAMETHASONE 6 mg IM q12 x 4 doses
What if the woman did not deliver after 14 days?
If the woman did not deliver after 14 days, from the time the steroids were given, a single rescue dose may be given to women who are <34 weeks AOG at risk of preterm delivery within 7 days.
Antenatal corticosteroids also has the added benefit of:
- Reducing the incidence of necrotizing enterocolitis & intraventricular hemorrhage
- Reduction in need for ventilatory support and NICU stay
- Reduction in the risk of infection
- Overall reduction in neonatal mortality
Management
Specific Therapy
- Ensure adequate ventilation & oxygenation
- Ensure adequate ventilation and oxygenation warmed & humidified using a HOOD
- to prevent atelectasis, pulmonary vasoconstriction and v/q mismatch
- continuous positive airway pressure (CPAP) via mask, nasal cannula or ET tube must be employed to provided positive end-expiratory pressure (PEEP) 4 to 6 cm H2O sedate the infant
- maintain arterial oxygen tension between 60 to 80 mmHg
- if the infant cannot maintain a PaO2 >50 mmHg while breathing 70 to 100% O2, or when FiO2 exceeds 0.40 on CPAP intubation and mechanical ventilation with PEEP is required
- other indications for mech vent: - Arterial pH <7.20
- PaCO2 >60 mmHg
- Severe persistent apnea
- the optimal mode of ventilation reduces risk of barotrauma remains unclear.
Based on avail literature, use of SYNCHRONIZED VOLUME-TARGETED VENTILATION with TIDAL VOLUMES set at 4 to 6 mL/kg with permissive hypercarbia is appropriate.
Regardless of the choice of ventilator, the goal is to minimize barotrauma and oxygen toxicity while still reaching target PaO2 and paCO2.
Blood gas monitoring every 4 to 6 hours with an Indwelling arterial line (umbilical_ may be contemplated.
Management
Supportive Care
- THERMOREGULATION
- FLUIDS
- NUTRIITION
- CONTINUOUS VITAL SIGNS MONITORING
- ANTIBIOTICS
- ELECTROLYTES
- ACID-BASE BALANCE
- BLOOD TRANSFUSION
- CARDIAC SUPPORT
- THERMOREGULATION - maintain in thermoneutral envt to minimize heat loss and maintain core body temperature —> reducing oxygen consumption, carbon dioxide production and caloric needs
- FLUIDS - should maintain in a slightly negative water balance since excessive fluid intake increase the risk of PDA, NEC, and BPD
- NUTRIITION - to cover both metabolic expenditure and growth
IV glucose 60 ml/kg on the 1st day; 80 to 100 ml/kg on the 2nd day
Monitor CBG every 12 hours - CONTINUOUS VITAL SIGNS MONITORING
- ANTIBIOTICS - obtain blood culture and treat with Ampicillin + Gentamicin until cultures are available
- ELECTROLYTES
- ACID-BASE BALANCE - limit NaHCO3 to 8 meq/kg/d to prevent hyeprnatremia
- BLOOD TRANSFUSION - if Hct <35 to maintain oxygen carrying capacity
- CARDIAC SUPPORT - inotropic agents like dopamine & dobutamine if needed
Management
- Surfactant replacement therapy
SURFACTANTS are indicated for those with:
- Pesistent Severe RDS - requiring a FiO2 of 0.40 or higher to maintain spO2 >90%
- Apneic patients - the standard technique for surfactant administration is through ET tube; may be complicated by transient airway obstruction or inadvertent instillation only into the right main bronchus
o2 saturation should be monitored since desaturation may occur
Less invasive measures include aerosolized surfactant, laryngeal mask airway aided delivery of surfactant, pharyngeal instillation or the use of thin intrathecal catheters
SURFACTANT PREPARATIONS include NATURAL and SYNTHETIC surfactants. Although both are effective, natural surfactants are superior since they contain SP-B and SP-C***
Natural surfactants - contain DPPC, neutral lipids and SP-B and SP-C
- Poractant Alfa (Curosurf) - porcine lung minced extract
- Calfactant (Infasurf) - bovine lung lavage extract
- Beractant (Survanta) - bovine lung minced extract
Synthetic surfactants
1. Colfosceril Palmitate (exosurf)
2. Lucinactant (Surfaxin) - discontinued
“Prophylactic dose” may be given immediately after birth of a premature infant
“rescue dose” is given during the 1st 24 hours of life after diagnosis of ROS established
